The current semiconductor technology requires semiconductor devices with higher integration as well as higher operational speed. In accordance with such demands, there is increasing need for a semiconductor device with a fine pattern.
In general, the contact hole is formed between conductive layers in order to electrically connect them. Then, the contact hole is filled with conductive material, which comes into contact with a substrate. According to such a conventional contact method, as shown in FIG. 1, an insulating film 2 is formed on the semiconductor substrate or conductive film 1, and the upper surface of the insulating film is coated with a photoresist film (not shown). Next, in order to expose a predetermined contact hole portion at the minimum size which can be attained by conventional or selected exposure equipment, the photoresist pattern 3 is formed by a photolithography process through exposure and development. The insulating film 2 exposed in the form of the photoresist pattern (not shown) is etched according to the conventional photolithography process, thereby forming the contact hole and exposing a predetermined portion of the semiconductor substrate or the conductive layer 1. Photoresist pattern is removed by a conventional method. Afterwards, a metal layer is deposited on the overall surface of the resultant structure so that the exposed semiconductor substrate is in contact with the metal layer.
In the contact forming process using the photolithography process as described above, it is well known that the formation of the contact hole using the photoresist pattern is closely related to the diffraction of light. For example, resolution, which is the minimum pattern width formed using the photolithography process, is an important variable and determined by the following Rayleigh's equation. EQU R=k(.lambda./NA)
Here, R is the resolution; .lambda. is an exposure wavelength, NA is the lens' numerical aperture of the exposure equipment, and k is a constant adjusted according to the process condition. As a variable in accordance with a process capability, k is about 0.7 in a mass production step. Furthermore, an I-line of a light source used mainly in the mass production step has a wavelength of about 0.356 .mu.m, and a G-line has a wavelength of 0.436 .mu.m. In the case where the numerical aperture of the lens of the general exposure equipment is 2, the width of the photoresist pattern is about 0.5 .mu.m to 0.6 .mu.m, according to the above equation.
However, in the case where photoresist pattern width produced by the above Rayleigh's equation is applied to semiconductor devices pursuing higher integration, there are the following problems.
As the effective channel length of the semiconductor device is reduced to 0.5 .mu.m or less, the size and depth of the junction region are also reduced in proportion to the effective channel length. Because of the smaller proportions, even a slight misalignment during the formation process of the contact hole can expose the junction region of the semiconductor substrate, and the gate electrode adjacent to the junction region is degraded. Thus, an interconnection on line can arise resulting in the shorting of the circuit elements.
In order to solve the aforementioned problem, it is necessary to increase the exposure wavelength and the lens' numerical aperture of the exposure equipment, according to the Rayleigh's equation. In order to achieve these increase, new and expensive exposure equipment is required, and accordingly the manufacturing cost of the device is increased.